The use of copper interconnect features is becoming increasingly popular in semiconductor integrated circuit devices and the like. Copper interconnect features such as vias and interconnect leads (also known as wires) are commonly formed using damascene processing methods. The use of copper as an interconnect material provides for increased device speed, and copper interconnect features include reduced line resistance compared to conventionally used materials such as aluminum and its alloys. Copper, however, has very high diffusion rates in metals and dielectrics, even at low temperatures. Copper diffusion can lead to leakage and reliability failures. One approach to preventing such copper diffusion and failures includes the introduction of barrier materials such as tantalum and tantalum nitride within the vias, trenches, and other openings in which the damascene copper interconnect structures are conventionally formed. The barrier materials encapsulate the copper within the openings. After a polishing operation is carried out to planarize the structure and form the damascene copper interconnect feature within the dielectric, however, the upper, polished copper surface is exposed. If this exposed copper surface is not encapsulated or otherwise covered, copper from the exposed copper surface may diffuse into or through conductive and/or dielectric materials formed over the copper interconnect structure.
One conventional technique for covering the copper surface and preventing copper diffusion is to form a silicon nitride or silicon carbide layer over the entire structure (including over the copper surface) prior to the subsequent deposition of further dielectric films over the copper structure. The silicon nitride or silicon carbide layer then necessarily forms part of the superjacent dielectric stack. This multilayered dielectric stack ostensibly requires additional processing operations to form the silicon nitride or silicon carbide layer. Furthermore, copper diffusion or electromigration may occur along the silicon carbide/copper or silicon nitride/copper interface and lead to reduced device reliability.
What is therefore required in the art is a method and structure for preventing copper electromigration along the copper/dielectric interface and copper diffusion into and through overlying dielectric and conductive materials.